Optical system including selectively activatable facets

ABSTRACT

In an embodiment, an apparatus is disclosed that includes at least one processor configured to determine a target portion of an eye motion box and to identify a facet of a light-guide optical element that is configured to direct a light beam comprising at least a portion of an image field of view toward the target portion of the eye motion box. The at least one processor is configured to identify a display region of an image generator that is configured to inject the light beam into the light-guide optical element at an angle that, in conjunction with the identified facet, is configured to direct the light beam toward the target portion of the eye motion box. The at least one processor is configured to selectively activate the identified facet and the identified display region to direct the light beam toward the target portion of the eye motion box.

BACKGROUND OF THE SPECIFICATION

The present disclosure relates to optical systems. More specifically,the present disclosure relates to optical systems having selectivelyactivatable facets that may, in some embodiments, be used in near-eyedisplay systems.

Optical systems such as near-eye display systems typically illuminatethe eye of a user with an image. In some cases, an optical system mayilluminate the entire eye or the entire pupil with a light beam of theimage regardless of where the pupil is located. In some cases, externallight may produce ghost images due to reflections by the optical system.However, illumination of the entire eye or the entire pupil may beinefficient and ghost images may be undesirable.

SUMMARY

In an embodiment, an apparatus is disclosed that comprises at least oneprocessor. The at least one processor is configured to determine atarget portion of an eye motion box and to identify a facet of aplurality of facets of a light-guide optical element. The identifiedfacet is configured to direct a light beam comprising at least a portionof an image field of view toward the target portion of the eye motionbox. The at least one processor is further configured to identify adisplay region of a plurality of display regions of an image generator.The identified display region is configured to inject the light beaminto the light-guide optical element at an angle that, in conjunctionwith the identified facet, is configured to direct the light beam towardthe target portion of the eye motion box. The at least one processor isfurther configured to selectively activate the identified facet and theidentified display region to direct the light beam toward the targetportion of the eye motion box.

In some embodiments, a method is disclosed comprising determining atarget portion of an eye motion box and identifying a facet of aplurality of facets of a light-guide optical element. The identifiedfacet is configured to direct a light beam comprising at least a portionof an image field of view toward the target portion of the eye motionbox. The method further comprises identifying a display region of aplurality of display regions of an image generator. The identifieddisplay region is configured to inject the light beam into thelight-guide optical element at an angle that, in conjunction with theidentified facet, is configured to direct the light beam toward thetarget portion of the eye motion box. The method further comprisesselectively activating the identified facet and the identified displayregion to direct the light beam toward the target portion of the eyemotion box.

In an embodiment, an optical system is disclosed. The optical systemcomprises a light-guide optical element comprising a plurality offacets. Each facet is selectively activatable between at least a firststate in which the facet is configured to allow a light beam to betransmitted therethrough and a second state in which the facet isconfigured to reflect the light beam. The facets are configured todirect light beams corresponding to an image field of view toward atarget portion of an eye motion box when in the second state. Theoptical system further comprises an image generator comprising aplurality of display regions. The display regions are selectivelyactivatable to inject light beams corresponding to the image field ofview into the light-guide optical element at different angles. Theoptical system further comprises a controller that is configured toidentify a facet of the plurality of facets. The identified facet isconfigured to direct a light beam comprising at least a portion of theimage field of view toward the target portion of the eye motion box. Thecontroller is further configured to identify a display region of theplurality of display regions. The identified display region isconfigured to inject the light beam comprising the at least a portion ofthe image field of view into the light-guide optical element at an anglethat, in conjunction with the identified facet, is configured to directthe light beam toward the target portion of the eye motion box. Thecontroller is further configured to selectively activate the identifiedfacet and the identified display region to direct the light beam towardthe target portion of the eye motion box.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description. In the drawings, like reference numbers indicateidentical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an example optical system with a firstfacet activated according to an embodiment.

FIG. 1B is a schematic diagram of an example image generator of theoptical system of FIG. 1A with a first display region activatedaccording to an embodiment.

FIG. 2A is a schematic diagram of the optical system of FIG. 1A with asecond facet activated according to an embodiment.

FIG. 2B is a schematic diagram of the example image generator of FIG. 1Bwith a second display region activated according to an embodiment.

FIG. 3A is a schematic diagram of the optical system of FIG. 1A with athird facet activated according to an embodiment.

FIG. 3B is a schematic diagram of the example image generator of FIG. 1Bwith a third display region activated according to an embodiment.

FIG. 4A is a schematic diagram of the optical system of FIG. 1A with afourth facet activated according to an embodiment.

FIG. 4B is a schematic diagram of the example image generator of FIG. 1Bwith a fourth display region activated according to an embodiment.

FIG. 5 is a table and chart illustrating sequential activation of thefacets and display regions of FIGS. 1A-4B over time according to anembodiment.

FIGS. 6A and 6B are schematic diagrams of the optical system of FIGS. 1Aand 1B illustrating the direction of light beams onto an eye using aneye tracking system according to an embodiment.

FIGS. 7A and 7B are schematic diagrams of the optical system of FIGS. 1Aand 1B illustrating the direction of light beams onto an eye without theuse of an eye tracking system according to an embodiment.

FIG. 8 is a schematic diagram of an example light-guide optical element(LOE) of the optical system of FIG. 1 and showing an available range offield of view (FOV) for a single activated facet according to anembodiment.

FIG. 9 is a schematic diagram of an example LOE of the optical system ofFIG. 1 and showing a difference between an FOV split by a facet and aconjugated FOV according to an embodiment.

FIG. 10A is a schematic diagram of an example optical system having anadditional LOE for 2-dimensional (2D) expansion according to anembodiment.

FIG. 10B is a schematic diagram of an example image projection assemblyof the optical system of FIG. 10A according to an embodiment.

FIG. 11A is a schematic diagram of the optical system of FIG. 10Aincluding a mixer according to an embodiment.

FIG. 11B is a schematic diagram of the example image projection assemblyof FIG. 10B including the mixer of FIG. 11A according to an embodiment.

FIG. 12 is a schematic diagram of an example LOE showing an externallight source creating ghost images on an eye according to an embodiment.

FIG. 13 is a schematic diagram of the LOE of FIG. 1 inhibiting lightfrom an external light source from creating ghost images on an eyeaccording to an embodiment.

FIG. 14 is a schematic diagram of the LOE of FIG. 1 inhibiting lightfrom an external light source from creating ghost images on an eyeaccording to another embodiment.

FIG. 15 is a schematic diagram of an example LOE showing light beamspropagating in the LOE creating ghost images by reflections off ofsemi-reflective facets according to an embodiment.

FIG. 16A is a schematic diagram of an example optical system having anadditional LOE for 2D expansion according to an embodiment.

FIG. 16B is a schematic diagram of an example image projection assemblyof the optical system of FIG. 16A having facets with selectivelyactivatable segments according to an embodiment.

FIG. 16C is a schematic diagram of an example image generator of theoptical system of FIG. 16A having selectively activatable displayregions according to an embodiment.

FIG. 17 is a flow diagram of an example process according to anembodiment.

DETAILED DESCRIPTION

In optical systems such as near-eye display systems, light beams areoutput from a display system to a target surface such as the eye of auser that is in close proximity to the display system. Often suchoptical systems illuminate the entire eye, or the entire pupil of theeye, when projecting an image. In some cases, such a blanketillumination of the eye or pupil can be costly in terms of powerefficiency for the near-eye display system, resulting in reduced batterylife or increased power consumption.

In some cases, external light sources may cause the optical system topresent ghost images to the eye. For example, light beams from externallight sources may enter the optical system and be directed onto the eyeat the same time as a target image generated by the optical system. Suchghost images can be distracting to a user, cause glare, or negativelyimpact the quality of the target image that is being projected onto theeye.

With reference to FIGS. 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B and 5 , anexample optical system 100 is described. Optical system 100 comprises animage projection assembly 110 and a controller 140. In some embodiments,optical system 100 may also comprise one or more of an eye trackingsystem 600 and a light source detection system 602.

Controller 140 comprises a computing device having one or moreprocessing devices, memory or other components. For example, controller140 may comprise a central processing unit (CPU), field-programmablegate array (FPGA), microcontroller, dedicated circuitry or any othercomponents. Controller 140 is configured to control a projection opticsdevice (POD) to generate and output images to a light-guide opticalelement (LOE) for projection to an eye as will be described in moredetail below.

In some embodiments, controller 140 may be integrated into imageprojection assembly 110 or integrated into a device comprising imageprojection assembly 110 such as, e.g., glasses, a head mounted displayor another device. In some embodiments, controller 140 may be locatedremote from image projection assembly 110. For example, image projectionassembly 110 may comprise a wired or wireless communication device thatis configured to communicate with controller 140. As an example,controller 140 may be included as part of a mobile device, or othercomputing device that is separate from image projection assembly 110 ora device including image projection assembly 110.

Eye tracking system 600 is optional and is configured to track thelocation of the pupil of an eye 180 of a user and provide correspondinglocation information to controller 140. In some embodiments, eyetracking system 600 may comprise, for example, a camera or other devicethat may be configured to track a location of the pupil or generateinformation that may be utilized to determine a location of the pupil.

Light source detection system 602 is optional and is configured todetect light sources that may impact optical system 100, e.g., the sun,streetlamps, headlights or other light sources, and to providecorresponding information to controller 140, e.g., a direction of thelight source, intensity of the light source or any other informationabout the light source. As an example, light source detection system 602may comprise a camera, infrared detector or any other device that isconfigured to detect light sources external to optical system 100 or togenerate information that may be utilized by controller 140 to identifyand determine the characteristics of a light source such as, e.g., thedirection, intensity or any other information about the light source.

Image projection assembly 110 comprises a projection optics device (POD)112 and a light-guide optical element (LOE) 114 and is configured toutilize 1-dimensional (1D) or 2-dimensional (2D) pupil expansion toproject an image onto an eye 180 of the user.

POD 112 comprises an image generator 200, collimating optics 300 orother components that are sometimes included in an image projectionassembly such as, e.g., a spatial light modulator (SLM). Some or all ofthese components may be arranged on surfaces of one or more polarizingbeamsplitter (PBS) cubes or other prism arrangements in someembodiments. Image generator 200 comprises one or more components thatprovide illumination, e.g., light beams, laser beams or other forms ofillumination, that correspond to an image to be projected onto eye 180of the user. For example, image generator 200 comprises light emittingdiodes (LEDs), an organic light emitting diode (OLED) display element, abacklit liquid crystal display (LCD) panel, a micro-LED display, adigital light processing (DLP) chip, a liquid crystal on silicon (LCOS)chip or other components.

In a case where POD 112 comprises an SLM (not shown), the SLM may beimplemented as a light emitting SLM comprising components such as, e.g.,an OLED display element, a backlit LCD panel, a micro-LED display, a DLPchip or another light emitting component, or may be implemented as areflective SLM comprising components such as, e.g., an LCOS chip. A beamsplitter cube block may be interposed between collimating optics and theSLM to allow delivery of illumination to the surface of the SLM. The SLMmay be configured to modulate the projected intensity of each pixel ofthe illumination to generate the image. For example, the SLM may providea light beam that is divergent in the plane of LOE 114, e.g., the planeof the major LOE surfaces 116 and 118 described below, from each pixelof the display.

Alternatively, POD 112 may include a scanning arrangement, e.g., afast-scanning mirror, which scans illumination from a light sourceacross an image plane of POD 112 while the intensity of the illuminationis varied synchronously with the motion on a pixel-by-pixel basis toproject a desired intensity for each pixel.

POD 112 also comprises a coupling-in arrangement for injecting theillumination of the image into LOE 114, e.g., a coupling-in reflector,angled coupling prism or any other coupling-in arrangement. In someembodiments, coupling between POD 112 and LOE 114 may include a directcoupling, e.g., POD 112 may be in contact with a portion of LOE 114, ormay include a coupling via an additional aperture expanding arrangementfor expanding the dimension of the aperture across which the image isinjected in the plane of LOE 114.

LOE 114 comprises a waveguide including first and second parallel majorLOE surfaces 116 and 118 and edges that are not optically active, asshown in, for example, FIGS. 1A-4B. LOE 114 also comprises acoupling-out arrangement 120 that is configured to direct theillumination out of LOE 114 for projection onto eye 180 of the user. Insome embodiments, coupling-out arrangement 120 is illustrated as aplurality of parallel surfaces, also referred to herein as facets 122 ₁,122 ₂, 122 ₃ and 122 _(4,)that are arranged within LOE 114 at an obliqueangle to major LOE surfaces 116 and 118 of LOE 114. Facets 122 ₁, 122 ₂,122 ₃ and 122 ₄ may also be referred to herein collectively orindividually as facets 122. While four facets 122 ₁, 122 ₂, 122 ₃ and122 ₄ are illustrated in FIGS. 1A-4B in an illustrative embodiment, LOE114 may alternatively comprise a larger number of facets 122 or asmaller number of facets 122 in other embodiments.

Each facet 122 is selectively activatable between a state in which thefacet 122 has a high transmissivity of light and a state in which thefacet 122 has a high reflectivity of light. As an example, in someembodiments, facet 122 ₁ may be activated to have 100% reflectivity and0% transmissivity and may be deactivated to have 0% reflectivity and100% transmissivity. In some embodiments, the amount of reflectivity andtransmissivity may be adjustable for each facet 122 such that, forexample, facet 122 ₁ may be adjusted to have partial reflectivity andpartial transmissivity, e.g., have 25% reflectivity and 75%transmissivity, 50% reflectivity and 50% transmissivity, 75%reflectivity and 25% transmissivity or any other amount of reflectivityand transmissivity. As an example, controller 140 may be configured toselectively activate and adjust the reflectivity and transmissivity ofeach facet 122. In some embodiments, controller 140 may be configured toselectively activate and adjust the reflectivity and transmissivity ofeach facet 122 for particular angles or ranges of angles of light beams,e.g., high transmissivity for some angles or a range of angles of lightbeams and high reflectivity for other angles or ranges of angles oflight beams.

Image generator 200 comprises display regions 202 ₁, 202 ₂, 202 ₃ and202 ₄ that are selectively activatable by controller 140 to generatecorresponding light beams L₁, L₂, L₃ and L₄ that enter LOE 114 andreflect off of major LOE surfaces 116 and 118 with different angles.Display regions 202 ₁, 202 ₂, 202 ₃ and 202 ₄ may also be referred toherein individually and collectively as display region(s) 202. Lightbeams L₁, L₂, L₃ and L₄ may also be referred to herein individually orcollectively as light beam(s) L. While four display regions 202 andcorresponding light beams L are shown in the example image generator 200of FIGS. 1B, 2B, 3B and 4B, image generator 200 may comprise a larger orsmaller number of display regions 202 and corresponding light beams L inother embodiments. Each display region 202 comprises one or more pixelsor other display elements that may be selectively activated bycontroller 140. In some embodiments, for example, each display region202 comprises a single pixel. In other embodiments, each display region202 may comprise a grouping of pixels, a horizontal line of pixels, avertical line of pixels or any other grouping of pixels.

As shown in FIGS. 1A-4B, for example, light beams L travel through LOE114 towards facets 122 by reflecting off major LOE surfaces 116 and 118.For example, major LOE surfaces 116 and 118 may provide total internalreflection (TIR) for any light beams L traveling through LOE 114. Lightbeams L travel through any inactive facets 122, e.g., due to the hightransmissivity of the inactive facets 122. When a light beam Lencounters an active facet 122, light beam L is redirected by the activefacet 122 out of LOE 114 due to the high reflectivity of the activefacet 122, e.g., towards eye 180.

FIG. 1A illustrates a first example scenario where display region 202 ₁and facet 122 ₁ are active and light beam L₁ generated by display region202 ₁ travels through LOE 114. In this scenario, display regions 202 ₂,202 ₃ and 202 ₄ and facets 122 ₂, 122 ₃ and 122 ₄ are inactive. Lightbeam Li reflects off major LOE surfaces 116 and 118, passing throughinactive facets 122 ₄, 122 ₃ and 122 ₂ in order before reflecting off ofactive facet 122 ₁ and being redirected towards eye 180.

FIG. 2A illustrates a second example scenario where display region 202 ₂and facet 122 ₂ are active and light beam L₂ generated by display region202 ₂ travels through LOE 114. In this scenario, display regions 202 ₁,202 ₃ and 202 ₄ and facets 122 ₁, 122 ₃ and 122 ₄ are inactive. Lightbeam L₂ reflects off major LOE surfaces 116 and 118, passing throughinactive facets 122 ₄ and 122 ₃ in order before reflecting off of activefacet 122 ₂ and being redirected towards eye 180. In this scenario,because facet 122 ₂ is active and fully reflective, e.g., 100%reflective, light beam L₂ does not reach facet 122 ₁. In someembodiments, facet 122 ₂ may not be fully reflective even when active.In such a case, light beam L₂ may reach facet 122 ₁ but is not reflectedbecause facet 122 ₁ is inactive.

FIG. 3A illustrates a third example scenario where display region 202 ₃and facet 122 ₃ are active and light beam L₃ generated by display region202 ₃ travels through LOE 114. In this scenario, display regions 202 ₁,202 ₂ and 202 ₄ and facets 122 ₁, 122 ₂ and 122 ₄ are inactive. Lightbeam L₃ reflects off major LOE surfaces 116 and 118, passing throughinactive facet 122 ₄ before reflecting off of active facet 122 ₃ andbeing redirected towards eye 180. In this scenario, because facet 122 ₃is active and fully reflective, e.g., 100% reflective, light beam L3does not reach facets 122 ₁ and 122 ₂. In some embodiments, facet 122 ₃may not be fully reflective even when active. In such a case, light beamL₃ may reach one or more of facets 122 ₁ and 122 ₂ but is not reflectedbecause facets 122 ₁ and 122 ₂ are inactive.

FIG. 4A illustrates a fourth example scenario where display region 202 ₄and facet 122 ₄ are active and light beam L₄ generated by display region202 ₄ travels through LOE 114. In this scenario, display regions 202 ₁,202 ₂ and 202 ₃ and facets 122 ₁, 122 ₂ and 122 ₃ are inactive. Lightbeam L₄ reflects off major LOE surfaces 116 and 118 before reflectingoff of active facet 122 ₄ and being redirected towards eye 180. In thisscenario, because facet 122 ₄ is active and fully reflective, e.g., 100%reflective, light beam L₄ does not reach facets 122 ₁, 122 ₂ and 122 ₃.In some embodiments, facet 122 ₄ may not be fully reflective even whenactive. In such a case, light beam L₄ may reach one or more of facets122 ₁, 122 ₂ and 122 ₃ but is not reflected because facets 122 ₁, 122 ₂and 122 ₃ are inactive.

As seen in FIGS. 1A-4B, while a different combination of display regions202 and facets 122 are active in each figure, the generated light beamsL₁, L₂, L₃ and L₄ are each directed toward the eye 180, but withdifferent angles. For example, the relative position of each facet 122and the pupil of eye 180 defines which portion of an image field of view(FOV) can be projected by that facet 122 towards the pupil of eye 180 byeach display region 202. In some embodiments, in order to optimize theenergy efficiency of optical system 100, only the portion of the imageFOV that can be projected by each facet 122 is generated by thecorresponding display region 202. For example, for a particular portionof the image FOV, controller 140 may activate only the display region202 and corresponding facet 122 that will direct that portion of theimage FOV to the location of the pupil of eye 180.

With reference to FIG. 5 , in some embodiments, combinations of displayregions 202 and facets 122 may be selectively and sequentially activatedto project different portions of the image FOV for each frame of thesame image onto eye 180.

As an example, facet 122 ₁ and display region 202 ₁ may be activated ata time T₁ to direct a first portion of the image FOV of a first frame oneye 180, facet 122 ₂ and display region 202 ₂ may be activated at a timeT₂ to direct a second portion of the image FOV of the first frame on eye180, facet 122 ₃ and display region 202 ₃ may be activated at a time T₃to direct a third portion of the image FOV of the first frame on eye180, facet 122 ₄ and display region 202 ₄ may be activated at a time T₄to direct a fourth portion of the image FOV of the first frame on eye180, facet 122 ₁ and display region 202 ₁ may be activated at a time T₅to direct the first portion of the image FOV of a second frame on eye180, facet 122 ₂, display region 202 ₂ may be activated at a time T₆ todirect the second portion of the image FOV of the second frame on eye180, facet 122 ₃ and display region 202 ₃ may be activated at a time T₇to direct the third portion of the image FOV of the second frame on eye180, facet 122 ₂, display region 202 ₂ may be activated at a time T₈ todirect the fourth portion of the image FOV of the second frame on eye180 and so on.

As described above, portions of the image FOV of the first frame of theimage may be sequentially generated and directed onto eye 180 duringtimes T₁-T₄ while the portions of the image FOV of the second frame ofthe image may be generated and directed onto eye 180 during times T₅-T₈.Times T₁-T₈ may comprise any unit of time that is configured to providea target framerate for projecting frames of an image onto eye 180. Forexample, times T₁-T₈ may be in milli-seconds (ms) or any other unit ofmeasure.

Because only one active facet 122 and one corresponding display region202 are utilized at a time to project a portion of the image FOV ontoeye 180 with the active facet 122 being fully reflective and all otherfacets 122 being fully transmissive, the energy efficiency of POD 112 isimproved over optical systems having static semi-reflective facets sincepotentially 100% or close to 100% of the light beam generated by imagegenerator 200 is reflected out of LOE 114 toward eye 180 by the activefacet 122.

For example, some LOEs comprise semi-reflective facets that areconfigured to direct light beams out of the LOE that propagate withinthe LOE at different angles. In these LOEs, only certain angles of lightbeams will be reflected by each facet while other angles will be allowedto pass through the facets. Because of this effect, portions of thelight provided to the LOE by the POD may be reflected by more than onefacet, even if those portions light are not directed toward the eye ofthe user which may result wasted power and inefficiencies in the POD.

In addition, the use of selectively activatable facets 122 and displayregions 202 enables optical system 100 to provide a larger availableimage FOV for each facet 122 as compared to optical systems having LOEswith static semi-reflective facets. For example, each staticsemi-reflective facet may only be able to provide light beams to the eyethat correspond to a particular image FOV depending on the angle atwhich they are reflective. Because facets 122 may be fully reflectivewhen activated, a larger available image FOV is possible because facets122 can redirect light from a larger number of angles.

In some embodiments, facets 122 may be activated by controller 140 insemi-reflective states that are similar to the static semi-reflectivefacets described above where only certain angles of light beams will bereflected by each facet 122 while other angles will be allowed to passthrough each facet 122 such that portions of the light provided to LOE114 by POD 200 may be reflected by more than one facet even if thoseportions of light are not directed toward the eye of the user. Forexample, facets 122 may be activated by controller 140 to mimic thefunctionality of the static semi-reflective facets described above insome embodiments.

With reference to FIGS. 6A and 6B, in some embodiments, controller 140may utilize location information received from eye tracking system 600to determine a location of the pupil 182 of eye 180 and activate thecorresponding combination of display regions 202 and facets 122 toproject portions of the image FOV toward a portion 184 of an eye motionbox (EMB) that corresponds to the determined location of pupil 182 ofeye 180. For example, the relationship between the portion of the imageFOV projected towards eye 180 by active facet 122 ₂ and thecorresponding display region 2022 of image generator 200 that generatesthe portion of the image FOV that is projected through this portion 184of the EMB is illustrated in FIGS. 6A and 6B.

Light beams 204 and 206 connect the edges of facet 1222 and pupil 182 ofeye 180. Eye tracking system 600 generates location informationcorresponding to the position of pupil 182 relative to LOE 114 andprovides the location information to controller 140. Using the locationinformation, controller 140 determines the angles and directions alongwhich light beams 204 and 206 need to travel relative to LOE 114 to beprojected onto portion 184 of the EMB that corresponds to the positionof pupil 182. For example, controller 140 may be configured to determinethe angles 208 and 210 that light beams 204 and 206 need to reflect offof facet 1222 relative to major LOE surface 116 of LOE 114. The angle212 between light beams 204 and 206 defines the extension of the imageFOV projected by facet 1222 into pupil 182. Angles 208 and 210 of lightbeams 204 and 206 relative to major LOE surface 116 may be converted,e.g., using geometrical optics laws such as, e.g., geometric laws oflight reflection and refraction, to corresponding angles of light beams204 and 206 with the projector optical axis 214 at the exit of the POD112. As shown in FIG. 6A, angle 208 corresponds to an angle 216 andangle 210 corresponds to an angle 218 at the exit of POD 112 relative toprojector optical axis 214. For example, in a system in which the imageFOV central direction is orthogonal to major LOE surface 116 whenejected towards the EMB or eye pupil, and in which the image FOV centraldirection coincides with the optical axis of POD 112, angle 216 is equalto 90 degrees minus angle 208 and angle 218 is equal to 90 degrees minusangle 210.

Distortion laws may then be applied to determine the coordinates X1 andX2 of activated display region 202 ₂ via the focal length of thecollimating optics 300 angle α, i.e., angle 218, and angle ⊕, i.e.,angle 216 according to equations (1) and (2) below:X1=ƒ×tan (α)   (1)X2=ƒ×tan (β)   (2)

In this manner, energy usage by image projection assembly 110 may beoptimized and energy efficiency of optical system 100 may be increasedsince the energy is used to illuminate only the location of pupil 182.

With reference to FIGS. 7A and 7B, in some embodiments, locationinformation about pupil 182 may not be available for use by controller140, e.g., if no eye tracking system 600 is present or active. In thisembodiment, the actual location of pupil 182 is unknown to controller140. In such a case, instead using portion 184 of the EMB thatcorresponds to the actual location of pupil 182, a larger portion 186 ofthe EMB is used for the calculations. In some embodiments, portion 186corresponds to the entire EMB in which pupil 182 can be located duringthe operation of optical system 100 while portion 184 corresponds toonly part of the EMB. Using portion 186 as the target instead of portion184, controller 140 may determine the angles corresponding to the neededlight beams in a similar manner to that described above for FIGS. 6A and6B and activate the corresponding facet 122 and display region 202accordingly.

In some embodiments, controller 140 may determine that multiple displayregions 202 need to be activated to project a portion of the image FOVtoward portion 186 of the EMB. In such a case, controller 140 may beconfigured to selectively activate each of the determined displayregions 202 or, in some embodiments, selectively activate only theselect pixels of each of the display regions 202 that are needed toilluminate portion 186 of the EMB, e.g., to activate a combined displayregion 220 as shown in FIG. 7B. For example, display region 220comprises a portion of display region 202 ₁ and a portion of 202 ₂. Insome embodiments, the activation of a combined display region 220 may beutilized with the embodiment of FIGS. 6A and 6B even where eye trackingsystem 600 is present. For example, the determined location of pupil 182may necessitate the activation of portions of multiple display regions202 by controller 140 in some embodiments.

In some embodiments, controller 140 may determine that multiple facets122 need to be sequentially activated for each display region 202 toprovide the corresponding image FOV to each possible location of pupil182 in EMB 186. For example, a particular display region 202 may beactivated by controller 140 to provide a particular image FOV or portionof the particular image FOV to eye 180. For the particular displayregion 202 that is being activated, each facet 122 is configured todirect the image FOV onto a different location when activated. In a casewhere there is uncertainty with respect to the location of pupil 182, atleast some of facets 122 may be activated sequentially to ensure thatthe corresponding image FOV is directed to a subset of locations ofpupil 182 in EMB 186.

In some cases, only some of facets 122 may be configured to direct lightfrom the particular display region 202 onto EMB 186 while other facets122 may be configured to direct light from the particular display region202 outside of EMB 186, e.g., depending on the angle of the light in LOE114. In some embodiments, only a grouping of facets 122 that areconfigured to direct light from the particular display region 202 ontoEMB 186 may be sequentially activated to direct the image FOV from theparticular display region 202 onto each portion of EMB 186 where pupil182 may be located while other facets 122 that will not direct the imageFOV onto EMB 186 for the particular display region 202 may not beactivated. In some embodiments, a different grouping of facets 122 mayneed to be sequentially activated for each display region 202 to directthe corresponding image FOV onto each portion of EMB 186, e.g., sinceeach display region 202 provides light at a different angle to LOE 114and facets 122.

With reference to FIG. 8 , in an illustrative embodiment, the availableimage FOV that can be projected toward eye 180 for an active facet 122of LOE 114 may be significantly larger than the image FOV that may beprojected by a static semi-reflective facet such as that described abovesince active facet 122 is fully reflective. This is because all lightgenerated by an active display region 202 will be reflected by the onlyactive facet 122 and will pass through any inactive facets 122regardless of the angle of the light beam since they are fullytransmissive. The available image FOV of the active facet 122 is limitedonly by the total internal reflection of major LOE surfaces 116 and 118of LOE 114 rather than which particular angles of light can be reflectedas in the case of the semi-reflective facets described above.

For example, as seen in FIG. 8 , light beams L₅ and L₆ are generated bycorresponding display regions of image generator 200 (FIG. 1A) and arereflected by major LOE surfaces 116 and 118 of LOE 114 until they reachactive facet 122. In this example, light beam Ls reflects off of majorLOE surface 116 at an angle 124 to the normal of major LOE surface 116while light beam L₆ reflects off of major LOE surface 116 at an angle126 to the normal of major LOE surface 116. Light beam L₅ is shownreflecting off of active facet 122 at a shallow angle while light beamL₆ is shown reflecting off of active facet 122 at a steep angle. In anembodiment, angle 124 is the maximum propagation angle of LOE 114 whileangle 126 is the total internal reflection critical angle of LOE 114.For example, angle 124 may comprise 90 degrees, 85 degrees or any othervalue. In some embodiments, the maximum available angle 124 may be basedon the manner in which light beams are injected into LOE 114. Angle 124and angle 126 together define the maximum available image FOV that canbe provided by an individual facet 122.

Example angles 124 and 126 illustrate an available image FOV that takesfull advantage of the entire active facet 122 and allows active facet122 to be utilized for projecting an image FOV onto eye 180 at anylocation within the EMB. For example, for any location of eye 180, thecorresponding display region 202 that is configured to generate a lightbeam that will reflect within LOE 114 at an angle that corresponds tothe location of eye 180 when reflected off of active facet 122 andrefracted by major LOE surface 116 as it passes through major LOEsurface 116 may be selectively activated to present an image FOV to eye180.

Because the available image FOV for each selectively activatable facet122 is larger than that of a static semi-reflective facet, in someembodiments, a smaller number of facets 122 may be utilized to providethe same image FOV coverage which also enhances the efficiency ofoptical system 100.

FIG. 9 illustrates an example FOV 136 that propagates in LOE 114 and aconjugated FOV 130. FOV 136 is reflected into conjugated FOV 130 as aresult of the total internal reflection of major LOE surfaces 116 and118 of LOE 114. As seen in FIG. 9 , an active facet 122 dividesconjugated FOV 130 into two parts, FOV 132 and FOV 134.

In LOEs having the static semi-reflective facets mentioned above, thesemi-reflective facets are not able to split the conjugated FOVpropagating in the LOE without impacting the resulting image. Forexample, a semi-reflecting coating often has a very high reflectivity atlarge angles of incidence. Because of this very high reflectivity,portions of conjugated FOV 130 that are propagating at angles close tothe angle of the semi-reflective facet are reflected by thesemi-reflective facet and contribute to the ghost images. In order toreduce the presence of such ghost images, an optical system having anLOE with semi-reflective facets may provide an image within either FOV134, e.g., at shallow angles, or FOV 132, e.g., an angle sufficientlylarge to not be reflected by the semi-reflecting coating, but not withinthe full conjugated FOV 130 up to and including angles that are close tothe angle of the facet.

In illustrative embodiments, facets 122 can be deactivated and madetransparent even at high angles of incidence such that conjugated FOV130 will propagate through them without generating ghost images. Thisresults in the ability to take advantage of conjugated FOV 130 togenerate a larger image FOV for active facet 122 as shown in FIG. 8 ascompared to the FOV in LOEs with semi-reflective facets. In one examplescenario, LOE 114 may comprise a refractive index of 1.8 and a criticalangle of 33.7 degrees. The FOV propagating within LOE 114 may compriseabout 51.3 degrees and the FOV output by an active facet 122 of LOE 114in this example scenario may comprise a FOV of about 93 degrees.

With reference to FIGS. 10A and 10B, an example optical system 400according to another embodiment is described. As illustrated in FIGS.10A and 10B, like elements have similar reference numbers to opticalsystem 100 of FIGS. 1A-4B. For example, optical system 400 comprises animage projection assembly 410 comprising a POD 412 and an LOE 414, acontroller 440 and other components similar to those described above foroptical system 100. LOE 414 comprises major LOE surfaces 416 and 418 anda coupling-out arrangement 420 that comprises facets 422 ₁, 422 ₂, 422 ₃and 422 ₄. In the embodiment of FIGS. 10A and 10B, image projectionassembly 410 further comprises an LOE 500 disposed between POD 412 andLOE 414.

LOE 500 comprises a coupling-out arrangement 502 comprising facets 504₁, 504 ₂, 504 ₃, 504 ₄, 504 ₅, 504 ₆ and 504 ₇ which may also becollectively and individually referred to herein as facet(s) 504. Whileillustrated as comprising seven facets 504 in the example optical system400 of FIGS. 10A and 10B, LOE 500 may alternatively comprise a larger orsmaller number of facets 504 in other embodiments.

LOE 500 and facets 504 are used for 2D expansion of the LOE exit pupil.In some embodiments, facets 504 may comprise static semi-reflectivefacets comprising dielectric coatings such as the semi-reflective facetsmentioned above. In other embodiments, facets 504 may alternativelycomprise selectively activatable facets that are similar to facets 122of FIGS. 1A-4B and may be selectively activatable by controller 440 in asimilar manner to that described above with reference to facets 122,e.g., to an inactive state with 100% transmissivity and 0% reflectivity,to an active state with 0% transmissivity and 100% reflectivity, or toanother state having partial transmissivity and partial reflectivity.

With reference to FIGS. 11A and 11B, another embodiment of opticalsystem 400 is described. In the embodiment of FIGS. 11A and 11B, imageprojection assembly 410 further comprises a mixer 506 that comprises asemi-reflecting surface inside LOE 414 which is parallel to major LOEsurfaces 416 and 418. Mixer 506 splits the light beams in LOE 414 asshown by the solid and dashed arrows in FIG. 11A. The splitting by mixer506 enables image projection assembly 410 to completely fill theaperture of LOE 414.

With reference to FIG. 12 , in an example comparative scenario, one ormore external light sources 700 and 702 may generate light beams thatenter into LOE 714. LOE 714 in this scenario comprises staticsemi-reflecting facets 722 ₁, 722 ₂, 722 ₃ and 722 ₄. As shown in FIG.12 , when light beam 724 from external light source 700 enters LOE 714,it is split at facet 7224 with a first portion 726 passing through facet722 ₄ and exiting LOE 714 and a second portion 728 reflecting off offacet 722 ₄ and propagating through LOE 714. As seen in FIG. 12 , whilefirst portion 726 does not affect eye 180, second portion 728 isdirected out of LOE 714 toward eye 180 by facet 722 ₂. The propagationand direction of second portion 728 of light beam 724 onto eye 180 byLOE 714 in this scenario may result in ghost images being projected ontoeye 180. It is important to note that, in most cases, ghost imagesresult from a reflection of light beams from external light sources bymultiple facets of an LOE where a reflection from a single facet doesnot on its own direct the light beam out of the LOE toward the eye of auser.

With reference to FIG. 13 , in another example scenario, LOE 114 isillustrated. In this example, because facet 122 ₄ is inactive, lightbeam 724 is not split by facet 122 ₄ and instead passes through LOE 114without affecting eye 180. In addition, because the active facet 122,facet 122 ₂ in this example scenario, is fully reflective, a light beam730 generated by external light source 702 reflects within LOE 114 butdoes not split and is not directed toward eye 180 by facet 122 ₂. Sincefacet 122 ₂ is the only active facet, no ghost images are produced bylight beams 724 and 730.

With reference to FIG. 14 , in another example scenario, collimatedlight beams 730 are generated by external light source 702 with eachlight beam 732, 734 and 738 entering different portions of LOE 114 atthe same angle. The light beams 730 experience Fresnel reflections onmajor LOE surface 116 of LOE 114, e.g., due to the angle at which theyare propagating within LOE 114. For example, because of the angle atwhich light beams 730 enter LOE 114, they will not pass through majorLOE surface 116 in the same manner that light beam 724 did in theexample scenario of FIG. 13 . In such a case, even having only a singleactive facet 122 ₂ may still result in a ghost image being directedtoward pupil 182 of eye 180, for example, as shown by light beam 734.However, if either of facets 122 ₁ and 122 ₃ were active, thecorresponding light beams 732 and 736 would not be directed toward pupil182 of eye 180 and no ghost image would occur.

The position of the external light source 700 may be determined bycontroller 140 using light source detection system 602 (FIG. 1A) whilethe position of pupil 182 may be determined by controller 140 using eyetracking system 600 (FIG. 1A). Based on the known positions of externallight source 700 and pupil 182, controller 140 is configured todetermine which facets 122 can project the ghost images onto pupil 182.In some embodiments, controller 140 may be configured to skip activationof those facets 122 that contribute to a ghost image due to externallight source 700 when generating an image. In some embodiments,controller 140 may be configured to adjust the reflectivity of thosefacets 122 that contribute to a ghost image due to external light source700 where, for example, the facets 122 can be set to a reflectivity ofless than 100% in order to attenuate the ghost image at a cost of havinga reduced available FOV for projection of a generated image onto pupil182.

With reference to FIG. 15 , in an example comparative scenario, an LOE814 receives a light beam 824 from a POD (not shown). In this examplecomparative scenario, LOE 804 comprises static semi-reflecting facets822 ₁, 822 ₂, 822 ₃ and 822 ₄. As light beam 824 propagates through LOE814, light beam 824 may be split by one or more of facets 822 intomultiple portions having different angles of propagation. For example,as shown in FIG. 15 , light beam 824 is split by semi-reflecting facet822 ₄ into a first portion 826, e.g., the projected image, thatcontinues along the same propagation path as light beam 824 and a secondportion 828, e.g., a ghost light beam, that has an altered propagationpath and angle. In some cases, the split portions 826 and 828 of lightbeam 824 may cause ghost images to be projected onto eye 180 by one ormore of the facets 822. For example, as seen in FIG. 15 , second portion828 is partially reflected by facet 822 ₃ onto eye 180 while firstportion 826 is partially reflected by facet 822 ₂ onto eye 180,resulting in the projection of both the image by first portion 826 and aghost image by second portion 828 on eye 180 at the same time.

In illustrative embodiments, the disclosed LOE 114 having selectivelyactivatable facets 122 overcomes this issue since only the facet thatwill direct the light beam onto eye 180 needs to be active such thatthere is no opportunity for light beams to be split. In addition,because the active facet may be set to 100% reflectivity while theinactive facets may be set to 100% transmissivity the light beamreceived from POD 112 will be fully reflected out of LOE 114 by theactive facet 122 and is not impacted by the inactive facets 122 in anymeaningful way that would cause ghost images.

With reference to FIGS. 16A-16C, an example embodiment of optical system400 is described. In the embodiment of FIGS. 16A-16C, image projectionassembly 410 further comprises an LOE 900 disposed between POD 412 andLOE 414.

LOE 900 comprises a coupling-out arrangement 902 comprising facets 904₁, 904 ₂, 904 ₃, 904 ₄, 904 ₅, 904 ₆ and 904 ₇ which may also becollectively and individually referred to herein as facet(s) 904. Whileillustrated as comprising seven facets 904 in the example optical system400 of FIG. 16A-16C, LOE 900 may alternatively comprise a larger orsmaller number of facets 904 in other embodiments.

LOE 900 and facets 904 are used for 2D expansion of the LOE exit pupil.In the embodiment of FIGS. 16A-16C, facets 904 comprise selectivelyactivatable facets that are similar to facets 122 of FIGS. 1A-4B and maybe selectively activatable by controller 440 in a similar manner to thatdescribed above with reference to facets 122, e.g., to an inactive statewith 100% transmissivity and 0% reflectivity, to an active state with 0%transmissivity and 100% reflectivity, or to another state having partialtransmissivity and partial reflectivity. In addition, in the embodimentof FIGS. 16A-16C, facets 904 further comprise selectively activatablesegments 908 such as, e.g., the active segment of facet 904 ₃ indicatedby the solid line, that may be separately activated or deactivated bycontroller 440 without activating the entire facet 904. In someembodiments, facets 422 of LOE 414 may also comprise selectivelyactivatable segments 910 such as, e.g., the active segment of facet 422₃ indicated by the solid line, that may be separately activated ordeactivated by controller 440 without activating the entire facet 422.

As shown in FIG. 16C, POD 412 comprises an image generator 1000 thatcomprises display regions 1002 arranged in a grid. In some embodiments,each display region 1002 may correspond to a pixel of image generator1000. In other embodiments, each display region 1002 may correspond to agrouping of pixels of image generator 1000. Each display region 1002 isselectively activatable by controller 440 to project an image into LOE900 via exit aperture 906. For example, in some embodiments, one or moredisplay regions 1002 may be activated to project an image for aparticular FOV.

As seen in FIG. 16B, for a single activated facet 904 and segment 908 inLOE 900 and a single activated facet 422 and segment 910 in LOE 414, theprojected FOV towards eye 180 along the X axis is defined by thelocation of pupil 182 and the exit aperture 906 of POD 412 in an opticalsystem with an eye tracking system 600 (FIG. 1A).

By knowing the position of pupil 182, the angles needed to direct lightbeams toward the position of pupil 182 may be calculated by controller440 in a similar manner to that described above for FIGS. 6A and 6B. Thecalculated angles define the display region 1002, facet 904, segment908, facet 422 and segment 910 that need to be activated to direct alight beam from exit aperture 906 toward a portion 912 of the EMB thatcorresponds to the determined location of pupil 182. In this embodiment,additional calculations may be needed due to the addition of LOE 900 ascompared to the calculations performed by controller 440 for theembodiment of FIGS. 6A and 6B. For example, the above mentioneddistortion laws of equations (1) and (2) may be utilized or expanded tocalculate the angle for each light beam from display region 1002 to exitaperture 906, from exit aperture 906 to segment 908, from segment 908 tosegment 910 and from segment 910 to portion 912 of the EMB.

In an optical system that does not have an eye tracking system 600, alarger portion 186 (FIG. 7A) of the EMB may be used to calculate thelight beam angles and directions in a similar manner to that describedabove with reference to FIGS. 7A and 7B.

With reference to FIG. 17 , an example process for operating the opticalsystem 100 comprising control of the selectively activatable facets 122and selectively activatable display regions 202 will now be described.The process may be performed at least in part by controller 140, eyetracking system 600, POD 112 and LOE 114 or may be performed at least inpart by any other portion of optical system 100.

The process of FIG. 17 comprises steps 1100 through 1106. While theprocess of FIG. 17 is described herein as having particular steps or aparticular order of steps, the process may alternatively perform thesteps in any order, may include additional steps, may include fewersteps or may only perform a portion of the steps described below inother embodiments.

At step 1100, controller 140 determines the target portion of the EMB.For example, in some embodiments, controller 140 may determine thetarget portion as portion 184 of the EMB using location informationobtained from eye tracking system 600 as described above with referenceto FIGS. 6A and 6B. In some embodiments, e.g., where eye tracking system600 is not included or unavailable, controller 140 may determine thetarget portion as portion 186 of the EMB as described above withreference to FIGS. 7A and 7B.

At steps 1102 and 1104, controller 140 identifies the facet 122 of LOE114 and the display region 202 of image generator 200 that areconfigured to direct a light beam comprising at least a portion of animage field of view toward the target portion of the EMB. For example,the facet 122 and corresponding display region 202 may be identified bycontroller 140 as described in the above embodiments. While steps 1102and 1104 are illustrated as being performed in a particular order, anyother order may be used. In addition, in some embodiments, steps 1102and 1104 may comprise a single step.

At step 1106, controller 140 selectively activates the identified facet122 and the identified display region 202 to direct the light beamtoward the target portion of the eye motion box, for example, as shownin FIGS. 1A-4B or the other embodiments described above.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements, if any, in the claims below areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The disclosed embodiments of the present invention have beenpresented for purposes of illustration and description but are notintended to be exhaustive or limited to the invention in the formsdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art without departing from the scope and spiritof the invention. The embodiments were chosen and described in order tobest explain the principles of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand the invention for various embodiments with variousmodifications as are suited to the particular use contemplated.

The invention claimed is:
 1. An apparatus comprising at least oneprocessor, the at least one processor being configured to: determine atarget portion of an eye motion box; identify one or more facets of aplurality of facets arranged within a light-guide optical element at anoblique angle to major surfaces of the light-guide optical element, theidentified one or more facets being configured to direct a light beamcomprising at least a portion of an image field of view toward thetarget portion of the eye motion box, wherein the identified one or morefacets is selectively activatable between at least a first state inwhich the identified one or more facets is configured to allow at leasta portion of the light beam to be transmitted through the identified oneor more facets and a second state in which the at least a portion of thelight beam is reflected by the identified one or more facets; identify adisplay region of a plurality of display regions of an image generator,the identified display region being configured to inject the light beaminto the light-guide optical element at an angle that, in conjunctionwith the identified one or more facets, is configured to direct thelight beam toward the target portion of the eye motion box; andselectively activate the identified one or more facets from the firststate to the second state and selectively activate the identifieddisplay region to direct the light beam toward the target portion of theeye motion box.
 2. The apparatus of claim 1, wherein each display regionof the plurality of display regions is configured inject a light beaminto the light-guide optical element at a different angle.
 3. Theapparatus of claim 2, wherein: the light beam comprises a first lightbeam; the identified one or more facets comprises a first facet of theplurality of facets; the display region comprises a first display regionof the plurality of display regions, the first facet and the firstdisplay region together defining a first combination, the first displayregion being configured to inject the first light beam into thelight-guide optical element at a first angle; the at least one processoris further configured to: identify a second facet of the plurality offacets and a second display region of the plurality of display regionsthat together define a second combination, the second display regionbeing configured to inject a second light beam comprising at least asecond portion of the image field of view into the light-guide opticalelement at a second angle that, in conjunction with the second facet, isconfigured to direct the second light beam toward the target portion ofthe eye motion box; and sequentially activate and deactivate the firstcombination and the second combination to direct the first light beamand the second light beam toward the target portion of the eye motionbox in sequence.
 4. The apparatus of claim 3, wherein sequentiallyactivating and deactivating the first combination and the secondcombination to direct the first light beam and the second light beamtoward the target portion of the eye motion box in sequence comprises:setting the first facet to the second state; setting the second facet tothe first-state; activating the first display region to inject the firstlight beam into the light-guide optical element at the first angle;setting the first facet to the first state; setting the second facet tothe second state; and activating the second display region to inject thesecond light beam into the light-guide optical element at the secondangle.
 5. The apparatus of claim 1, wherein determining the targetportion of the eye motion box comprises: obtaining location informationfrom an eye tracking system, the eye tracking system being configured tomonitor a location of a pupil of an eye; and determining the targetportion of the eye motion box based at least in part on the obtainedlocation information.
 6. The apparatus of claim 1, wherein: the one ormore facets comprises a first facet; the plurality of facets comprise afirst plurality of facets; the light-guide optical element comprises afirst light-guide optical element; the at least one processor is furtherconfigured to identify a second facet of a second plurality of facets ofa second light-guide optical element, the second light-guide opticalelement being disposed between the image generator and the firstlight-guide optical element; the identified display region is configuredto inject the light beam into the first light-guide optical element viathe second light-guide optical element to direct the light beam towardthe target portion of the eye motion box in conjunction with the firstfacet and the second facet; and selectively activating the identifiedone or more facets and the identified display region to direct the lightbeam toward the target portion of the eye motion box comprisesselectively activating the first facet, the second facet and theidentified display region to direct the light beam toward the targetportion of the eye motion box.
 7. The apparatus of claim 1, wherein: theidentified one or more facets comprises a first facet; the at least oneprocessor is further configured to: determine that an external lightsource is injecting an external light beam into the light-guide opticalelement; and selectively deactivate a second facet of the plurality offacets based at least in part on the determination that the externallight source is injecting the external light beam into the light-guideoptical element.
 8. The apparatus of claim 7, wherein selectivelydeactivating the second facet comprises one of setting the second facetto a fully transmissive state and setting the second facet to apartially transmissive state.
 9. The apparatus of claim 7, wherein:determining that the external light source is injecting the externallight beam into the light-guide optical element comprises obtaining,from a light source detection system, location information correspondingto the external light source; and selectively deactivating the secondfacet of the plurality of facets based at least in part on thedetermination that the external light source is injecting the externallight beam into the light-guide optical element comprises: determiningthat the external light beam is directed toward the second facet basedat least in part on the location information; and selectivelydeactivating the second facet based at least in part on thedetermination that the external light beam is directed toward the secondfacet.
 10. The apparatus of claim 1, wherein: the one or more facetscomprises a plurality of segments, each segment of the plurality ofsegments being separately activatable to direct light beams from theimage generator; identifying the one or more facets comprisesidentifying a segment of the plurality of segments that is configured todirect the light beam toward the target portion of the eye motion box;and selectively activating the identified one or more facets comprisesselectively activating the identified segment to direct the light beamtoward the target portion of the eye motion box, at least one othersegment of the one or more facets being inactive when the identified oneor more facets is selectively activated.
 11. A method comprising:determining a target portion of an eye motion box; identifying one ormore facets of a plurality of facets arranged within a light-guideoptical element at an oblique angle to major surfaces of the light-guideoptical element, the identified one or more facets being configured todirect a light beam comprising at least a portion of an image field ofview toward the target portion of the eye motion box, wherein theidentified one or more facets is selectively activatable between atleast a first state in which the identified one or more facets isconfigured to allow at least a portion of the light beam to betransmitted through the identified one or more facets and a second statein which the at least a portion of the light beam is reflected by theidentified one or more facets; identifying a display region of aplurality of display regions of an image generator, the identifieddisplay region being configured to inject the light beam into thelight-guide optical element at an angle that, in conjunction with theidentified one or more facets, is configured to direct the light beamtoward the target portion of the eye motion box; and selectivelyactivating the identified one or more facets from the first state to thesecond state and selectively activating the identified display region todirect the light beam toward the target portion of the eye motion box.12. The method of claim 11, wherein: the light beam comprises a firstlight beam; the identified one or more facets comprises a first facet ofthe plurality of facets; the display region comprises a first displayregion of the plurality of display regions, the first facet and thefirst display region together defining a first combination, the firstdisplay region being configured to inject the first light beam into thelight-guide optical element at a first angle; and the method furthercomprises: identifying a second facet of the plurality of facets and asecond display region of the plurality of display regions that togetherdefine a second combination, the second display region being configuredto inject a second light beam comprising at least a second portion ofthe image field of view into the light-guide optical element at a secondangle that, in conjunction with the second facet, is configured todirect the second light beam toward the target portion of the eye motionbox; and sequentially activating and deactivating the first combinationand the second combination to direct the first light beam and the secondlight beam toward the target portion of the eye motion box in sequence.13. The method of claim 12, wherein sequentially activating anddeactivating the first combination and the second combination to directthe first light beam and the second light beam toward the target portionof the eye motion box in sequence comprises: setting the first facet tothe second state; setting the second facet to the first state;activating the first display region to inject the first light beam intothe light-guide optical element at the first angle; setting the firstfacet to the first state; setting the second facet to the second state;and activating the second display region to inject the second light beaminto the light-guide optical element at the second angle.
 14. The methodof claim 11, wherein: the identified one or more facets comprises afirst facet; the plurality of facets comprise a first plurality offacets; the light-guide optical element comprises a first light-guideoptical element; the method further comprises identifying a second facetof a second plurality of facets of a second light-guide optical element,the second light-guide optical element being disposed between the imagegenerator and the first light-guide optical element; the identifieddisplay region is configured to inject the light beam into the firstlight-guide optical element via the second light-guide optical elementto direct the light beam toward the target portion of the eye motion boxin conjunction with the first facet and the second facet; and the methodfurther comprises selectively activating the identified one or morefacets and the identified display region to direct the light beam towardthe target portion of the eye motion box comprises selectivelyactivating the first facet, the second facet and the identified displayregion to direct the light beam toward the target portion of the eyemotion box.
 15. The method of claim 11, wherein: the one or more facetscomprises a first facet; and the method further comprises: determiningthat an external light source is injecting an external light beam intothe light-guide optical element; and selectively deactivating a secondfacet of the plurality of facets based at least in part on thedetermination that the external light source is injecting the externallight beam into the light-guide optical element, the selectivedeactivation of the second facet comprising one of setting the secondfacet to a fully transmissive state and setting the second facet to apartially transmissive state.
 16. The method of claim 11, wherein: theone or more facets comprises a plurality of segments, each segment ofthe plurality of segments being separately activatable to direct lightbeams from the image generator; identifying the one or more facetscomprises identifying a segment of the plurality of segments that isconfigured to direct the light beam toward the target portion of the eyemotion box; and selectively activating the identified one or more facetscomprises selectively activating the identified segment to direct thelight beam toward the target portion of the eye motion box, at least oneother segment of the one or more facets being inactive when theidentified one or more facets is selectively activated.
 17. An opticalsystem comprising: a light-guide optical element comprising a pluralityof facets, each facet being selectively activatable between at least afirst state in which the facet is configured to allow a light beam to betransmitted through the facet and a second state in which the facet isconfigured to reflect the light beam, the plurality of facets beingconfigured to direct light beams corresponding to an image field of viewtoward a target portion of an eye motion box when in the second state;an image generator comprising a plurality of display regions, thedisplay regions being selectively activatable to inject light beamscorresponding to the image field of view into the light-guide opticalelement at different angles; and a controller that is configured to:identify one or more facets of the plurality of facets, the identifiedone or more facets being configured to direct a light beam comprising atleast a portion of the image field of view toward the target portion ofthe eye motion box; identify a display region of the plurality ofdisplay regions, the identified display region being configured toinject the light beam comprising the at least a portion of the imagefield of view into the light-guide optical element at an angle that, inconjunction with the identified one or more facets, is configured todirect the light beam toward the target portion of the eye motion box;and selectively activate the identified one or more facets from thefirst state to the second state and selectively activate the identifieddisplay region to direct the light beam toward the target portion of theeye motion box.
 18. The optical system of claim 17, wherein: the opticalsystem further comprises a light source detection system, the lightsource detection system being configured to provide information about anexternal light source to the controller; and the controller is furtherconfigured to: determine that the external light source is injecting anexternal light beam into the light-guide optical element based at leastin part on the information provided by the light source detectionsystem; and selectively deactivate a second facet of the plurality offacets based at least in part on the determination that the externallight source is injecting the external light beam into the light-guideoptical element, the selective deactivation of the second facet beingconfigured to inhibit the external light beam from reflecting off of thesecond facet as it passes through the light-guide optical element. 19.The optical system of claim 17, wherein: the one or more facetscomprises a plurality of segments, each segment of the plurality ofsegments being separately activatable to direct light beams from theimage generator; identifying the one or more facets comprisesidentifying a segment of the plurality of segments of the identified oneor more facets that is configured to direct the light beam toward thetarget portion of the eye motion box; and selectively activating theidentified one or more facets comprises selectively activating theidentified segment of the identified facet to direct the light beamtoward the target portion of the eye motion box, at least one othersegment of the one or more facets being inactive when the identified oneor more facets is selectively activated.